1. Field of the Art
This invention relates to a coil shaft which is particularly suitable for use as a flexible rotation transmission member of a control cable or the like, and a method for fabricating such coil shafts.
2. Prior Art
Control cables, with a rotary member at a distal end, generally have a flexible rotation transmission shaft fitted in a flexible sleeve. As a proximal end of the flexible transmission shaft is turned about its axis, the rotation is transmitted to the other fore distal end of the flexible shaft to which a rotary member is connected. The proximal end of the flexible shaft is connected to a rotational drive mechanism. The flexible sleeve is rotatable relative to the flexible transmission shaft, and fixedly connected to a non-rotatable member at least at its one end, preferably at its opposite ends. The rotational drive mechanism is provided with rotational drive means like an electric motor thereby to turn the proximal end of the flexible transmission shaft about its axis. The rotation of the proximal end of the flexible transmission shaft is followed by the rotary member which is connected to the fore distal end of the flexible transmission shaft. If necessary, the flexible transmission shaft can be rotated manually.
In the case of a rotation transmitting control cable of this sort, rotation has to be transmitted quickly and securely from one to the other end of a flexible transmission shaft which is fitted in a flexible sleeve. Besides, the flexible transmission shaft should be flexibly bendable in arbitrary directions, and should be able to transmit rotations even in a bent form securely with less resistance to rotation and smoothly under a smaller load.
Considering the general requirements as mentioned above, it has been the usual practice to employ, as a flexible transmission shaft of a control cable, a coil shaft which is formed by helically winding spring type metal wires. In order to transmit rotation more securely and accurately, the flexible transmission shaft is at least constituted by a coil shaft of a double coil construction having inner and outer coils. It has also been known in the art to employ a flexible transmission shaft of a triple coil construction especially for the purpose of transmitting rotations in both forward and reverse directions. Further, in order to prevent delays in transmitting rotation to a rotary member and to stabilize operation of the rotary member, the metal wires of the coil shaft are wound tightly in such a way that the interstices between the individual helices are completely closed. Further, each coil of the coil shaft can be constituted by either a single wire winding or a multiple-wire winding having a plural number of wires arranged flatly side by side in the fashion of a strip.
No matter whether a coil shaft is of a single wire winding type or a multiple-wire winding type, tightly wound coils are flexible in bending directions and capable of transmitting rotations quickly and securely to a fore distal end of the coil shaft. Namely, in a tightly wound state, a coil is no longer contractible in length, so that, upon applying a rotational force to a proximal end of the coil in a tightening direction, it is tightened into a substantially rigid from its proximal to fore distal end without undergoing changes in diameter. Therefore, the rotational force can be transmitted securely to the distal end to which a rotary member is connected. The coil shaft is flexibly bendable, so that, when bent, interstices are opened up between helices on the outer side of a bent portion. However, this does not affect the rotation transmitting capability of the coil shaft because helices on the inner side of a bent portion are tightly pressed to each other all the more.
This sort of flexible transmission shaft of a control cable, which can be constituted by a single coil shaft or double or triple coaxial coil shafts, is normally fitted in a flexible sleeve as mentioned above. The gap width between the flexible transmission shaft and the flexible sleeve is held to a minimum since radial vibrations will occur to the flexible transmission shaft during rotation if there is a conspicuous difference between the outside diameter of the flexible shaft and the inside diameter of the flexible sleeve. When a control cable is flexed into a bent state, the flexible sleeve and the flexible transmission shaft within the flexible is flexed into a similar shape separately from each other. When in a bent state, the flexible sleeve is stretched on the outer side of a bent portion and contracted on the inner side of the bent portion, which is somewhat flattened in cross-sectional shape. In contrast, the tightly wound coils of the flexible transmission shaft undergoes substantially no changes neither in diameter nor in pitch of helices on the inner side of the bent portion, although the pitch of helices on the outer side of the bent portion is broadened to some extent. Namely, as a control cable is flexed into a bent form, the flexible sleeve is freely deformable but the flexible transmission shaft is considerably restricted in deformability. Especially, when a coil shaft is bent, a reaction force occurs in the coil shaft in a linear direction to resist a bending force. This resistance to a bending force becomes extremely large particularly in the case of a flexible transmission shaft which is constituted by multiple coil shafts.
For the reasons as stated above, when the control cable is bent, the flexible transmission shaft within the cable is partially pressed against an inner surface of the flexible sleeve. Accordingly, when the control cable is in a bent state and the flexible transmission shaft is pressed against an inner surface of the flexible sleeve, rotation of the flexible transmission shaft is met by a large resistance due to sliding contact of the flexible transmission shaft and sleeve. As a consequence, it becomes difficult for the flexible transmission shaft to transmit rotations smoothly, suffering from troubles such as increased load, irregular rotations and vibrations.
In addition, the internal cavity of a tightly wound coil shaft is substantially in a closed state, so that it is often found difficult to supply a liquid into the coil shaft which is fitted in a flexible sleeve. For instance, when there is a necessity for sealing a fluid in a hermetically closed coil shaft, this cannot be accomplished easily especially in the case of a multiple coil shaft which requires to replace air residues between inner and outer coils completely by a filling fluid.
With the foregoing situations in view, it is an object of the present invention to provide a coil shaft which is simple in construction and easy to manufacture, and which is improved in flexibility in bending directions.
It is another object of the present invention to provide a coil shaft which can transmit rotations smoothly under a light load when applied as a flexible rotation transmission shaft, despite freedom in bending flexibility.
It is still another object of the present invention to provide a coil shaft which permits to fill thereinto a fluid like a liquid from outside.
According to the present invention, in order to achieve the above-stated objectives, there is provided a multi-wire coil shaft having a plural number of metal wires helically wound together in intimately parallel relation with each other, the multi-wire coil shaft comprises coarsely wound portions where having helices of said wires are relatively spaced apart and being provided in or between tightly wound portions to take the shape of a partially coarsely wound coil shaft.
According to the present invention, there is also provided a method for fabricating a partially coarsely wound coil shaft as mentioned above, which essentially comprises the steps of: arranging a plural number of unit metal wires and at least one dummy wire intimately side by side and in parallel relation with each other like to present a shape of a single flat metal strip; helically winding the strip of wires around a round core to form a tightly wound coil shaft with helices of adjacent wires are tightly closed to each other; and removing the dummy wire from the multi-wire coil shaft to obtain a partially coarsely wound coil shaft.
The above and other objects, features and advantages of the present invention will become apparent from the following particular description of the invention, taken in conjunction with the accompanying drawings which show by way of example preferred embodiments of the invention. Needless to say, the present invention should not be construed as being limited to the particular forms shown.